The present invention relates to a high power television transmitter, and more particularly, to a television transmitter employing a high power klystron.
In a prior art television transmitter employing a klystron, the klystron beam current is set to a lower level in order to save power consumption and, in other words, to improve the klystron power efficiency. The lower level setting of the klystron beam current leads to a non-linear input-output characteristic of the klystron, and, thus, non-linear distortion appears in the output television signal. Therefore, in order to compensate for the non-linear distortion, a pre-distortion (pre-correction) circuit is inserted in the preceding stage.
According to another prior art television transmitter, the klystron beam current is further decreased during an active video period in order to further improve the klystron power efficiency, but is increased during only a sync period to stretch a sync signal. Such beam current control is performed by controlling the anode voltage of the klystron and the television transmitter using this method has been known as the "Anode Pulser System". This system was introduced at the 30th NAB Engineering Conference, Mar. 21-24, 1978. This system makes the input-output characteristic of the klystron further deteriorate and requires a pre-correction circuit having larger correction capabilities.
In the above-described prior arts transmitters, when higher power efficiency is required, the linearity of the input-output characteristic becomes worse, so that the amount of correction needed in the pre-correction circuit is increased in accordance with the degree of improvement of the power efficiency. As a result, sufficient correction becomes impossible because the input-output characteristic varies because of a change in a level of a supply voltage and because of a change in a klystron condition or attribute in accordance with a time lapse. This adversely affects the standard of the output television signal to be transmitted. Particularly, the luminance linearity is adversely affected by the change in the input-output characteristic (gain) of the klystron.